1. Field of the Invention
The present invention relates to a structure having a surface which reduces turbulence problems existing within the boundary layer of a fluid moving with respect to the surface.
2. Description of the Prior Art
The prior art describes various structures for controlling phenomena due to the interaction of a boundary layer of a fluid in motion with respect to a surface and notably turbulence phenomena.
These structures can be formed by surfaces provided with grooves present in the turbulence region. The axis of the grooves extends in the direction of flow of the fluid. The purpose of these grooves is to reduce the turbulence phenomena existing within the boundary layer of the fluid in motion and, by reducing friction between the surface and the fluid, to minimize pressure drops.
Experiments described in the prior art indicate pressure drop decreases up to 7% for example.
The grooves or pressure drop reduction means can have various geometries, and the number thereof can be selected as a function of the transportation conditions and/or of the nature of the fluid so as to obtain a minimum of pressure drops.
The grooves exhibit for example a slot type rectangular profile or a V-shaped profile.
The prior art also mentions the advantageous use of grooves of cylindrical shape, which can allow the obtaining of fluid anchoring effects, thus preventing development of the turbulence phenomenon in the boundary layer of the flowing fluid.
The expression "boundary layer" refers to a zone wherein a fluid is flowing in a pipe for example close to the wall or to the inner surface of this pipe, wherein the velocity gradient is the highest.
Another structure configuration considered in the prior art associates longitudinal grooves (in the direction of flow of the fluid) with a device arranged and suspended with respect to these grooves, the purpose of the latter being to "break" the swirls of great amplitude whereas the longitudinal grooves will act on the swirls of low amplitude. Such an association is however complex and bulky.
It has also been considered to use more complex geometries than a simple succession of identical grooves.
For example U.S. Pat. No. 5,386,955 describes a specific layout of similar slots or grooves. The slots of various sizes are arranged, according to a selected layout and sequence, in order to inhibit swirls of different scales within the boundary layer of the fluid.
However, such a device with an alternation of fins of different heights does not benefit locally by an addition of the effects (turbulence attenuation) resulting therefrom.